In general, a wheel loader or other such construction vehicle is equipped with what is called an HST (hydro-static transmission), with which an engine drives a hydraulic pump, and a travel hydraulic motor is driven by the hydraulic fluid discharged from the hydraulic pump.
With an HST type of construction vehicle such as this, the speed and traction of the vehicle can be controlled by controlling the engine speed, the volume of the hydraulic pump, and the volume of the travel hydraulic motor.
For example, International Laid-Open Patent Application Publication No. 2005/098148 and Japanese Laid-Open Patent Application Publication No. 2004-144254 disclose work machines (construction vehicles) or the like with which better fuel economy can be attained by varying the absorption torque of the hydraulic pump as dictated by the working situation and so forth.
Although not technology related to an HST type of wheel loader, Patent Literature 1 discloses a construction machine (hydraulic excavator) with which fuel economy is improved by switching the absorption torque of the hydraulic pump while evaluating the working situation. Meanwhile, Patent Literature 2 discloses a wheel loader that travels by driving an HST motor with hydraulic fluid discharged from an HST pump driven by an engine.